Reading the recent ScienceAlert article "For the first time, living cells have formed carbon-silicon bonds", it is stated that despite the relative abundance of silicon in the surface of the Earth, there are no silicon based lifeforms.

Specifically, the article asserts:

Why silicon has never be incorporated into any kind of biochemistry on Earth has been a long-standing puzzle for scientists, because, in theory, it would have been just as easy for silicon-based lifeforms to have evolved on our planet as the carbon-based ones we know and love.

I have read the question and answers "Why are we carbon-based?", which looks at the importance of carbon, what I am seeking information of is why carbon and why not silicon in the first place. So, therefore my question:

Why is it thought that silicon based lifeforms never flourished on Earth?

  • 1
    $\begingroup$ You might be interested in this $\endgroup$ Nov 26 '16 at 14:13
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    $\begingroup$ Keep in mind that there might have been silicon based lifeforms on Earth, but we do not know as we did not find them. It is estimated that 99.99% of all species that ever lived on Earth are extinct. $\endgroup$ Nov 26 '16 at 15:25
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    $\begingroup$ Well, diatoms do use silicon dioxide to form their cell walls, and some grasses incorporate it, so silicon is incorporated into biochemistry. $\endgroup$
    – jamesqf
    Nov 26 '16 at 19:20
  • $\begingroup$ Good points, I have replaced 'developed' with 'flourished' $\endgroup$
    – user27892
    Nov 27 '16 at 3:20
  • $\begingroup$ I dislike the use of "currently accepted" with regard to "theory" and something as speculative as the chemistry of life forms. If you are interested in theories, ask about them, but beware of trying to find comfort in things that other people "accept". I have edited your question to a form I think more suitable for a scientific forum. $\endgroup$
    – David
    Dec 4 '16 at 20:31

At temperatures above -195C, "C" wins the day. "Si" based chemistry may be more versatile than carbon in some environments, for example in a frozen nitrogen atmosphere.

Silicon accounts for 43% of rocks, Carbon is less than 0.1 percent, except that carbon is similar to water for reactivity and dissolving stuff, and organic "C" compounds are a molecular sludge like flowing-dissolved-stone, room-temperature-lava: tar/margarine/oil/diesel/glucose/alcohols/acetone are sludgy, liquid, the molecules can rotate, flow, coalesce... Carbon molecules are fluid, sludgy, rotating, pivoting, kind of lego material, whereas silicone chemistry doesn't flow, it vaporises and precipitates out of any flowing state.

Carbon reacts with both the molecules of water, O and H, and almost everything else, to make millions and millions of compounds. Silicon can't bond H. It's like the difference in between lego technic and lego. Try making a robot from lego!

That gives life millions of times more chemistry building blocks compared to silicone, and permits life to interact with water. Silicon life can't really interact with water.

  • 10/1 cosmic abundance of carbon vs silicon

  • A carbonaceous contrite meteorite can contain 70 extraterrestrial amino acids and other compounds including carboxylic acids, hydroxy carboxylic acids, sulphonic and phosphonic acids, aliphatic, aromatic and polar hydrocarbons, fullerenes, heterocycles, carbonyl compounds, alcohols, amines and amides.

  • If you put silicon in a flask with, metals, sulphur, nitrogen, water, etc, and do the same with graphite, and you mix and heat them all up, the carbon will tend to make a vast population of larger sludge molecules, tars, formadehyde, amino acids, and the silicon will tend to form rocky crystals, as found in geology.

  • SiO2 is sand, quartz, very unreactive, takes a lot of energy to make it, whereas CO2 is a relatively reactive solube compound.

  • Silane SiH4 is the equivalent of Methane CH4, but SiH4 oxidizes instantly in contact with water and oxygen and air and is totally unstable, not naturally occuring, and it's difficult to make it, it combusts and becomes elemental silicon and water.

  • A silicate rich meteorite will only contail a wide array of silicate minerals, which are simpler, mineralogical, unreactive substances compared to organic chemistry that can exist in a meteorite.

  • Carbon forms double electron bonds a lot easier than silicon because it is smaller and lighter with a small atomic radius.

  • Silicone carbide SiC is a very rare mineral which illistrates Silicon's fussiness in making bonds.

  • Silicon-hydrogen molecules react spontaneously with water and they exist more easily in suphuric acid, which kindof limits silicone to a square root of the combination possibilities available to carbon. The H reactions give it that extra connection ability, any time a carbonate molecule becomes unstable, it absorbs an H and it's stable. Silicone can't do that.

  • Silicon doesn’t want to let go of Oxygen, but it doesn’t want to attach to hydrogen. try burning or dissolving quartz and silicates, compared to carbonates and "C-H" compounds = organic compounds.

  • An AI life-form could make good use of silicon: it's unreactivity with water means that a silicon transistor brain can exist anywhere in frozen space, using metals and electricity for the animal's functions, and avoiding water. A robotic species of life would more probably be made of silicone, so if some alien life forms land on earth, they will probably be transistor and metal electric beings rather than carbon based ones.

Wikipedia page.


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